1. Field of the Invention
The invention is directed to tooling for machining operations and, more particularly, directed to zero centerline toolholder assembly that is substantially aligned at a non-perpendicular angle with respect to a longitudinal axis of the work piece during machining operations.
2. Description of the Related Art
Toolholder assemblies, such as milling and turning cutters, that perform machining operations on work pieces, are well known in the art. Typically, the toolholder assembly includes one or more cutting inserts that are mounted around the outer periphery of the cutter body for producing a series of metal-shaving cuts on a work piece.
Referring now to FIG. 2, a conventional toolholder assembly 100 includes a cutting tool 102, such as a cutting insert, is held by a toolholder 104. The toolholder 104 can be releasable secured within a tool spindle 106 by a shank 116 that is rotated by a spindle motor (not shown). The tool spindle 106 can be of a quick change type as described in U.S. Pat. No. 6,415,696, the entire contents of which is incorporated herein by reference. For example, a spindle clamping unit (not shown) may be used to releasably secure the shank 116 of the toolholder 104 to the tool spindle 106.
The toolholder 104 may have a support portion 112 with a pocket 114 for receiving the cutting insert 102 therein. The cutting insert 102 may be retained in the pocket 114 by a means well-known in the art, such as a clamp, or the like. As seen in FIG. 2, a central, longitudinal axis, LC, or centerline of the cutting insert 102 (and support portion 112) forms a non-zero angle, α, which respect to the central, longitudinal axis, LT, or centerline of the toolholder 104. The toolholder 104 may also includes a body portion 118 that extends from a tool rest 110 when the toolholder 104 is installed in the tool rest 110.
For CNC machining operations, the tool spindle 106 may be free to fix and hold the toolholder 104 and other tools in a predetermined holding state, and is free to rotate, drive and position around a rotational axis (axial center), CT2. When the toolholder 104 is installed in the tool rest 110, a central, longitudinal axis, LT, or centerline of the toolholder 104 corresponds to the rotational axis, CT2, of the tool rest 110. In addition, the tip of the cutting insert 102 that engages the work piece, 102 extends from the tool spindle 106 by a tool length, L, of approximately 5.9 inches (150 mm).
During machining operations, a work piece 102 is generally held by a chuck 122 with chuck jaws 124 for rotation in the direction, W, in a manner known in the art. When the work piece 102 is installed in the chuck jaws 124, the work piece 122 has a longitudinal axis, LW, along its centerline that is perpendicular to the longitudinal axis, LT, or centerline of the toolholder 104. It should also be noted that the direction of cut, as shown by the arrow, is along the Z-axis and is parallel to the longitudinal axis, LW, or centerline of the work piece 122 and perpendicular to the longitudinal axis, LT, or centerline of the toolholder 104. In addition, it should be noted that the centerline, LT, of the toolholder 104 and the rotational axis, CT2, of the tool rest 110 corresponds to the axis, P, perpendicular to the centerline, LW, of the work piece 102.
The inventors of the present invention have determined that the main component of cutting force is a tangential force that acts in a direction perpendicular to the top of the cutting insert 102. The next highest component of the cutting force is a feed force, which is generally about one-half (½) of the tangential force. The feed force usually acts in a direction opposite of the direction of cut (i.e., parallel to the Z-axis or centerline, LW, of the work piece 102 in FIG. 2). The next highest component of the cutting force is a radial force, which is generally about one-quarter (¼) of the tangential force, and acts in a direction perpendicular to the tangent point at which a nose radius 102a of the cutting insert 102 contacts the work piece 122. In FIG. 2, the radial force is along the same direction as the tool length, L, and toward the spindle housing 108. Therefore, the tangential load has the highest effect on the torque loading of the joint between the toolholder 104 and the tool spindle 106. A torque loading is developed by the tangential load and the radial offset of this load (i.e, the radial distance from the nose radius 102a of the cutting insert 102 to the centerline, LT, of the tool), and is perpendicular to tool length, L. In FIG. 2, the combination of the feed and radial forces provides an undesirable force component of about 26.6 degrees, for example, in the cutting plane that tends to try to pull the toolholder 104 out of the clamping unit of the tool spindle 106. In addition, the forces exerted on the toolholder 104 may cause a deflection of the toolholder 104 that is directly proportional to the tool length, L. Unfortunately, any error associated with the mounting connection between the toolholder 104 and the tool spindle 106 or deflection of the toolholder 104 can cause errors in the alignment of the cutting insert 102 with the work piece 102.
Thus, there is a need to provide a cutting tool orientation that minimizes or eliminates the torque on the cutting tool during machining operations, as well as reducing or eliminating the radial error associated with the connection of the toolholder with the toolholder spindle.